1. Field of the Invention
The present invention relates to a fuel cell-based generator having a gas generator for producing a reaction gas containing hydrogen and fuel cells that receive a supply of the reaction gas from the gas generator, and a method of generating electricity with the fuel cells.
2. Description of the Related Art
Fuel cells are a known device for directly converting the chemical energy of a fuel to electrical energy. Each fuel cell generally includes an electrolyte membrane interposed between a pair of electrodes. The surface of one electrode is exposed to a hydrogen-containing gaseous fuel, while the surface of the other electrode is exposed to an oxygen-containing gas. The fuel cell utilizes the electrochemical reactions occurring on these electrodes and takes electrical energy out of the electrodes.
A known gas generator for producing a gaseous fuel supplied to the fuel cell is a reformer that reforms methanol to steam (for example, JAPANESE PATENT LAID-OPEN GAZETTE No. 5-21079). Steam reforming of methanol in the reformer is carried out through the following chemical reactions: EQU CH.sub.3 OH.fwdarw.CO+2H.sub.2 -21.7 kcal/mol (1) EQU CO+H.sub.2 O.fwdarw.CO.sub.2 +H.sub.2 +9.8 kcal/mol (2) EQU CH.sub.3 OH+H.sub.2 O.fwdarw.CO.sub.2 +3H.sub.2 -11.9 kcal/mol(3)
As clearly understood from the equation (3) representing the reforming reaction, the reaction products by steam reforming are theoretically only hydrogen and carbon dioxide at the molar ratio of 3:1. In the actual state, however, the reaction does not proceed 100% ideally, and carbon monoxide as a by-product and non-reacted methanol exist after the reaction.
In the fuel cells, carbon monoxide is adsorbed by platinum or a platinum alloy, which functions as a catalyst on the electrode for receiving the gaseous fuel, thereby deteriorating the catalytic function of platinum. This phenomenon is generally referred to as poisoning of the catalyst. Methanol, on the other hand, passes through the electrolyte membrane and reaches the other electrode to react with oxygen included in the oxygen-containing gas, thereby lowering the potential on the oxygen electrode. Methanol also deteriorates durability of pipes constituting a flow path of gaseous fuel.
In known fuel cell-based generator systems, the utilization ratio of the gaseous fuel in the fuel cells is limited to 60 to 80%, in order to minimize the problems due to carbon monoxide and methanol. The problem of poor energy efficiency accordingly arises in such known fuel cell-based generator systems.